1. Field of the Invention
The present invention pertains to a pressure support system and method of treating disordered breathing, and, in particular, to bi-level auto-titration pressure support system and to a method of automatically titrating a pressure support system to optimize the inspiratory and expiratory pressure delivered to the patient to treat the disordered breathing while otherwise minimizing the delivered pressure for patient comfort.
2. Description of the Related Art
It is well known that many individuals suffer from disordered breathing during sleep. Obstructive sleep apnea (OSA), for example, is a common example of such disordered breathing suffered by millions of people through the world. OSA is a condition in which sleep is repeatedly interrupted by an inability to breathe, which occurs due to an obstruction of the airway; typically the upper airway or pharyngeal area. Obstruction of the airway is generally believed to be due, at least in part, to a general relaxation of the muscles which stabilize the upper airway segment, thereby allowing the tissues to collapse the airway.
Those afflicted with OSA experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of OSA include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Sleep apnea sufferers may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Even if a patient does not suffer from a complete obstruction of the airway, it is also known that adverse effects, such as arousals from sleep, can occur where there is only a partial obstruction of the airway. Partial obstruction of the airway typically results in shallow breathing referred to as a hypopnea. Other types of disordered breathing include upper airway resistance syndrome (UARS) and vibration of the airway, such as vibration of the pharyngeal wall, commonly referred to as snoring. It is also known that snoring can accompany closure of the airway leading to UARS, hypopnea, or apnea. Thus, snoring serves as an indicator that the patient is experiencing abnormal breathing.
It is known to treat such disordered breathing by applying a continuous positive air pressure (CPAP) to the patient's airway. This positive pressure effectively “splints” the airway, thereby maintaining an open passage to the lungs. It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing cycle, or varies with the patient's effort, to increase the comfort to the patient. This pressure support technique is referred to a bi-level pressure support, in which the inspiratory positive airway pressure (IPAP) is delivered to the patient is higher than the expiratory positive airway pressure (EPAP).
It is further known to provide a positive pressure therapy in which a continuous positive pressure is provided to the patient, and where the level of this pressure is automatically adjusted based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea or upper airway resistance. This pressure support technique is referred to as an auto-titration type of pressure support, because the pressure support device seeks to provide a pressure to the patient that is only as high as necessary to treat the disordered breathing.
Examples of conventional auto-titration pressure support systems are disclosed in U.S. Pat. Nos. 5,245,995 to Sullivan et al.; 5,259,373; 5,549,106, and 5,845,636 all to Gruenke et al.; 5,458,137 and 6,058,747 both to Axe et al.; 5,704,345; 6,029,665; and 6,138,675 all to Berthon-Jones; 5,645,053 to Remmers et al.; and 5,335,654; 5,490,502, 5,535,739, and 5,803,066 all to Rapoport et al. All of these conventional pressure support systems, with the exception of U.S. Pat. No. 5,645,053 to Remmers et al., are reactive to the patient's monitored condition. That is, once a condition occurs that indicates abnormal breathing, the system alters the pressure support to treat this condition. The present inventors discovered, however, that this treatment technique may not be suitable for all patients, and may cause the system to unnecessarily react to mild, temporary anomalies.
Furthermore, these auto-titration pressure support systems typically attempt to treat one condition of the patient, such as snoring or a flow limitation in the patient's inspiratory waveform. It is believed that this micro, target treatment, approach, focusing on one or two conditions, fails to provide an adequate treatment for a patient, which, in essence, is a very complicated system, affected by a variety of variables.
In addition, these conventional auto-titration systems present different approaches to detecting a condition of the patient. Each approach attempts to improve the ability to detect conditions of the patient that are truly indicative of a breathing disorder. However, each approach is believed to be limited in its ability to monitor and treat a wide population of patients in a robust manner.
Finally, conventional auto-titration pressure support systems are CPAP systems, and, as such, deliver a constant pressure that is the same during the patient's inspiratory and expiratory cycle. This approach, while acceptable to many patients, may not provide the optimum pressure support therapy or comfort for all patients.